This is a two-arm, randomized, multicenter, double-blind, phase III study to compare the clinical efficacy and safety of the combination of zdv, 3tc and idv to the combination of zdv and 3tc. The substitution of d4t for zdv will be allowed in both treatment arms after 24 weeks at the investigator's discretion (with the approval of the study chair/vice chairs) if a subject is showing signs or symptoms related to disease progression short of a primary study endpoint. This substitution (4dt for zdv) will be allowed at any time during treatment if a subject is intolerant to zdv.